Typically, dollies are made of relatively heavy, solid wood rectangles or wood slats with a caster fastened on the underside of each corner. These prior art dollies used, for example, metal corner plates or anchoring plates to add strength to the dolly frame, such as disclosed in U.S. Pat. No. 1,184,079 to D'Arcy and U.S. Pat. No. 2,414,277 to Shepard, Jr. et al. However, these plates are insufficient, in that they only provide reinforcement to a limited area, that is, only at the corners of the dolly. Another disadvantage of this construction is that the dolly caster is typically fastened with four bolts in order to maintain the rigidity of the dolly frame. Since all the bolts must be removed in order to disassemble the dolly, any repair or replacement of a worn element is a time consuming job.
Plastic dollies are preferable to wooden dollies as plastic is easier to clean and is less dense than wood. Thus plastic dollies are lightweight. Plastic dollies are also often cheaper than wooden dollies and are easier to manufacture. However, plastic dollies suffer from a lack of strength. Absent strengthening devices, a plastic dolly is not as strong as a wooden dolly.
U.S. Pat. No. 4,060,252 to Mowery and U.S. Pat. No. 4,103,857 to Levenhagen both disclose one piece plastic transfer devies. Mowery shows a plastic dolly with plastic strengthening ribs formed on the underside of the dolly. Levenhagen discloses a one piece plastic pallet having a steel rod for reinforcing the perimeter of the pallet. The primary disadvantage to these devices is that they are expensive to use since the entire device must be scrapped when only a portion of it is damaged.